Even with on prem solutions, I would hope that most websites are behind a load balancer with at least two instances. Storing session state on the web server hasn’t been something that I’ve ever done and I have been developing websites since at least 2002.

Legacy applications may not be websites, and might be stateful (or so I am told).

But how many store data locally as opposed to in a database? Even for stateful applications, if you have the source code, you could put an http listener on it for your target group to ping as a health check and put your data on FSx. If the app became unhealthy, kill the server and bring a new instance up. Have a minimum and maximum of one.

I wouldn’t go that far though. I would probably use something like Consul to do a local health check first and restart the app if it dies and then do the target group/health check as a second level check.

I was thinking more like some off-the-shelf solution purchased years ago that is something of a black box to those that operate it... subtle failure modes, lack of instrumentation, and opaque inner state.

Agreed but IT bosses just picks up these keywords and start throwing them around as benefits of cloud. Heck I had a CIO getting excited about moving to micro services when his entire landscape had only COTS application.